During fabrication of semiconductor devices, many layers are deposited on semiconductor wafers while they are situated in furnaces. Targeted deposition areas are often not precisely controlled. Thus, deposited material accumulates on walls of the furnace, as well as on the semiconductor wafers, where it is desired. Furthermore, during deposition, the furnace tubes accumulate the material which is deposited. During fabrication, steps are taken to clean the tubes and walls of the furnace, in order to avoid obstruction of depositions due to large accumulations of prior-deposited materials. Prior-deposited materials are also unwanted in a fabrication furnace because they tend to introduce impurities into subsequently-deposited layers.
As multiple layers are formed in semiconductor devices, individual layers may also need to be cleaned before the next layer is formed or before surface modification is done. Numerous preclean procedures exist for use prior to semiconductor surface modification in batch furnaces, including wet chemical cleans, hydrogen (H.sub.2) bakes and hydrofluoric acid (HF) vapor cleans. Preclean procedures are important to both reduce native oxide and remove other contaminants, such as residual organic and metallic impurities.
One desire, to ensure a low cost of batch production of ultra large scale integrated (ULSI) semiconductor devices, is to clean the surfaces in-situ, or in other words, without moving the semiconductor wafers into a different device specifically for cleaning. Given the large number of wafers being used for semiconductor integrated circuit (IC) manufacturing, which are being processed in batch-type furnaces, the cleaning of furnace tubes and precleaning of wafers at different processing stages becomes difficult. It is expensive and time consuming to move and precisely align the wafers to a separate cleaning area between formation of different layers. The transfer also increases the chances of contamination, or requires increased expense in preventing contamination and reduces throughput.
In-situ cleans have been accomplished somewhat by using H.sub.2 bakes and HF vapor cleans in standard cluster types of vertical and horizontal batch furnaces. However, to achieve uniformity of the clean, high temperatures (1,000 to 1,200 degrees Celsius) are required for the H.sub.2 bake and chemicals must be utilized to increase the corrosion rate in a HF vapor clean. Such high temperatures, as is well known, increase the thermal budget and cause further undesired impurities, as well as the potential for structural degradation. In the high volume production of semiconductor devices, the cost, time, and throughput of devices is extremely important, and each has a great affect on profitability. There is a need for reducing the cost of IC fabrication, while still maintaining a long useful life of the fabrication equipment and effectively cleaning surfaces on the wafers. There is a further need for an effective cost reduced in-situ cleaning method for the production of semiconductor devices. There is also a need to provide such in-situ cleaning for furnaces capable of processing large batches of semiconductor devices.